This invention relates to a self-switching valve for producing from a constant pressure fluid source a series of repetitive fluid pulses, which valve is self switching that is it does not require any outside power source other than the pressure supply to effect the switching action, the valve preferably providing a high speed and variable switching action.
One example of a technology which requires a valve of this type is that relating to the injection of liquid such as fertilizer into the ground from a fluid injection nozzle mounted above the ground. This intermittent action of high speed liquid jets into the ground has been shown to increase plant quality and productivity. For this purpose it is desirable that a valve be provided which transforms a constant 28 MPa pressure supply into a pulsating output of the same pressure but of variable pulse duration and frequency.
Currently the technology used in this field includes electrically actuated solenoid valves. Solenoid valves offer a variable open time and frequency simply by changing the nature of the input signals. Adjustment of these two parameters gives the operator (or an automatic timing control system) the flexibility to change both the injection quantity and spacing on-the-fly to match the injection equipment operation with the ground requirements and a changing ground speed. However solenoid valves generally leak and switch too slowly contributing to an ineffective and short system life. Another possibility includes valves which are ground driven, but these do not provide an adjustable open time and operating frequency which is independent of ground speed.
There is a demand therefore for an improved valve for this particular function, but the present invention is not limited to this particular function and the valve of the present invention may be used in other applications that require either a pulsating high pressure or force such as the descaling of pipes, a pressure actuated jack hammer or vibration excitation.
A search of valves effecting this particular function has revealed a number of prior art arrangements as follows:
SU Patent 420811 (Konoplev) discloses a poppet type valve, designed to work with gas, which is spring biased in one direction (closed) and displaced (opened) in the opposed direction by fluid pressure generated by flow from an inlet to a control chamber. However the fluid flow is controlled by a solenoid so that the valve requires an external power source in addition to that of the fluid inlet pressure supply. In addition the valve is relatively complicated with several moving parts thus increasing cost and reliability problems. PA1 U.S. Pat. No. 5,000,516 (Kolle) discloses a valve for generating high pressure pulses for demolishing rock and the like. This arrangement includes an accumulator into which fluid is pumped from a high pressure source through an inlet chamber. When the source is closed off and the inlet vented to atmosphere, the pressurized fluid in the accumulator rapidly opens a popper valve and fluid discharges at high pressure through an outlet. It is therefore necessary to provide an outside source of power to operate the valving arrangement which closes off the inlet source and opens the connection to atmosphere. PA1 An article by Kwok in the Instrument Society of America Conference dated Oct. 15th to 18th 1973 paper No. 73-830 discloses a liquid operated oscillator which uses the inertia in a fluid column to effect opening and closing of a diaphragm type valve to generate the pulsation in the output. Neither of the above oscillators by Kwok is suitable for producing the ground injection pulses with which the present invention is concerned nor provides any technique for varying the pulse frequency or duration which is highly desirable for such pulses. PA1 Voisekhovskii et al in a paper entitled "The use of pulsed two-dimensional high-speed liquid jets for breaking up exhausted assemblies of fuel elements of atomic power stations" translated from Atomnaya Energiya, Vol. 68, No. 6, pp. 443-445, June 1990 discloses briefly an arrangement for the generation of pulsed water fountains which is believed to have been used in a research project.
U.S. Pat. No. 4,267,856 (Kwok) discloses a fluid oscillator which generates a pulsating flow by using a ball which alternately blocks the mouth of one of two output ducts which are in a conical pressure chamber.